An orchid is the largest and most diverse family of flowering plants. Since an orchid is graceful in its floral morphology and blooms for 1-4 months, this plant is considerably popular with the public and widely used in decorations. Additionally, an orchid is the largest flower for export in Taiwan.
A flowering plant usually has a sepal, a petal, a stamen, and a pistil in sequence from the outside to the inside of its flower. In view of molecular biology, the flower is developed following the so-called “ABC model.” Expression of A genes characterizes the sepal; co-expression of A genes and B genes characterizes the petal; co-expression of B genes and C genes characterizes the stamen; expression of C genes characterizes the pistil. See Plant Mol Biol. 2000; 42(1): 115-49.
Although an orchid belongs to a flowering plant, its floral development is complicated without an explanation of the “ABC model.” Generally, the floral morphology of an orchid is classified into the following three categories: wild type, big-lip mutant, and peloric mutant. An orchid with a wild type floral morphology is shown on the left side of FIGS. 1A-1C, and its flower has two petals, one lip, three sepals, and one gynostemium. The two petals are symmetrical with each other, and the lip is distinct from each petal. An orchid with a big-lip mutant floral morphology is shown on the right side of FIG. 1C, and its lip is petal-like as compared with that of the plant with a wild type floral morphology. An orchid with a peloric mutant floral morphology is displayed on the right side of FIGS. 1A-1B, and its petals or sepals are lip-like relative to those of the plant with a wild type floral morphology. The floral morphology may have an effect on the plant's commercial value. It usually takes 1-3 years to cultivate an orchid, and the plant's floral morphology is usually ascertained during the late stage of cultivation. For such reason, if an orchid's floral morphology is predicted at the early stage of cultivation, and the plant having a non-marketable floral morphology is thrown away, the cost of unnecessary cultivation, such as time, labor, and money, is saved.